A new automatic ice-fabric analyzer which uses image-analysis techniques

Abstract

An automatic ice-fabric analyzer has been developed, which can determine individual ,-axis orientations by image-analysis techniques. The analyzer consists of four major components: a sample stage, a pair of crossed polaroids, a charge coupled device (CCD) camera and a light source. Both the sample stage and the crossed polaroids can be rotated independently of each other by the stepping motors controlled by a personal computer (PC). Measurements are conducted as follows. An ice thin section is set on the sample stage and then the crossed polaroids are rotated. Thin-section images are recorded by the PC at intervals of 2° of rotation. From the image-intensity (gray value) dataset of each crystal in the thin section the extinction angles of individual crystals can be determined. Similarly, eight other extinction angles of individual crystals are obtained from eight other CCD camera positions with respect to the thin section: Finally, the .-axis orientation of individual crystals is calculated by using these extinction angles. With this technique, all crystals within the view of the CCD camera can be analyzed at the same time. In addition, with image-processing techniques the individual crystals are recognized automatically and other parameters, such as grain-size and grain shape, can be measured simultaneously. Textural studies of Dome Fuji (Antarctica) ice cores have been conducted with this analyzer.

Performance and applications of an automated c-axis ice-fabric analyzer

“…Alley, from T. H. Jacka and D. S. Russell-Head, 1987, 1994, 1997, 1999. This technique is ideally suited to smaller ice thin sections, and to our knowledge has not yet been used to look at large numbers of thin sections from ice cores.…”

“…Also, refraction corrections are not included in their analysis. Wilen (2000) developed a technique for automatic icefabric analysis conceptually similar to that of Wang and Azuma (1999) but substantially different in detail. One important difference is that Wilen's technique includes refraction corrections, allowing the sample to be viewed at larger angles.…”

“…Wang and Azuma (1999) recently pioneered an automated technique for analyzing large ice thin sections. Their technique involves acquiring a large number of images of the ice viewed at different orientations through crossed polarizers as the polarizers are rotated through 360³.…”

Ice crystal <i>c</i>-axis orientation and mean grain size measurements from the Dome Summit South ice core, Law Dome, East Antarctica

“…In the time since these measurements were made considerable technological advances in the instruments available to measure crystal orientations have occurred (e.g. Yun and Azuma, 1999;Wilen et al, 2003;Wilson et al, 2007;Wilson and Peternell, 2011). Modern instruments provide several benefits over the universal stage including (i) higher resolution, enabling small-scale differences in crystallographic orientations within individual grains to be detected, (ii) the ability to spatially map c-axis orientations, (iii) automated operation and a significantly higher speed of determining orientations, and (iv) lower levels of uncertainty in both caxis azimuth and colatitude.…”

A new technique for ice-fabric analysis

“…Alley, fromT. H. Jacka and D. S. Russell-Head, 1987, 1997, 1999, but practical applications are still almost entirely based on the traditional Rigsby stage (Rigsby, 1951), as standardized and described by Langway (1958).…”